456 research outputs found
Type IIn supernovae at z ~ 2 from archival data
Supernovae have been confirmed to redshift z ~ 1.7 for type Ia (thermonuclear
detonation of a white dwarf) and to z ~ 0.7 for type II (collapse of the core
of the star). The subclass type IIn supernovae are luminous core-collapse
explosions of massive stars and, unlike other types, are very bright in the
ultraviolet, which should enable them to be found optically at redshifts z ~ 2
and higher. In addition, the interaction of the ejecta with circumstellar
material creates strong, long-lived emission lines that allow spectroscopic
confirmation of many events of this type at z ~ 2 for 3 - 5 years after
explosion. Here we report three spectroscopically confirmed type IIn
supernovae, at redshifts z = 0.808, 2.013 and 2.357, detected in archival data
using a method designed to exploit these properties at z ~ 2. Type IIn
supernovae directly probe the formation of massive stars at high redshift. The
number found to date is consistent with the expectations of a locally measured
stellar initial mass function, but not with an evolving initial mass function
proposed to explain independent observations at low and high redshift.Comment: 8 pages, 2 figures, includes supplementary informatio
Discovery of a Supernova Explosion at Half the Age of the Universe and its Cosmological Implications
The ultimate fate of the universe, infinite expansion or a big crunch, can be
determined by measuring the redshifts, apparent brightnesses, and intrinsic
luminosities of very distant supernovae. Recent developments have provided
tools that make such a program practicable: (1) Studies of relatively nearby
Type Ia supernovae (SNe Ia) have shown that their intrinsic luminosities can be
accurately determined; (2) New research techniques have made it possible to
schedule the discovery and follow-up observations of distant supernovae,
producing well over 50 very distant (z = 0.3 -- 0.7) SNe Ia to date. These
distant supernovae provide a record of changes in the expansion rate over the
past several billion years. By making precise measurements of supernovae at
still greater distances, and thus extending this expansion history back far
enough in time, we can distinguish the slowing caused by the gravitational
attraction of the universe's mass density Omega_M from the effect of a possibly
inflationary pressure caused by a cosmological constant Lambda. We report here
the first such measurements, with our discovery of a Type Ia supernova (SN
1997ap) at z = 0.83. Measurements at the Keck II 10-m telescope make this the
most distant spectroscopically confirmed supernova. Over two months of
photometry of SN 1997ap with the Hubble Space Telescope and ground-based
telescopes, when combined with previous measurements of nearer SNe Ia, suggests
that we may live in a low mass-density universe. Further supernovae at
comparable distances are currently scheduled for ground and space-based
observations.Comment: 12 pages and 4 figures (figure 4 is repeated in color and black and
white) Nature, scheduled for publication in the 1 January, 1998 issue. Also
available at http://www-supernova.lbl.go
Long gamma-ray bursts and core-collapse supernovae have different environments
When massive stars exhaust their fuel they collapse and often produce the
extraordinarily bright explosions known as core-collapse supernovae. On
occasion, this stellar collapse also powers an even more brilliant relativistic
explosion known as a long-duration gamma-ray burst. One would then expect that
long gamma-ray bursts and core-collapse supernovae should be found in similar
galactic environments. Here we show that this expectation is wrong. We find
that the long gamma-ray bursts are far more concentrated on the very brightest
regions of their host galaxies than are the core-collapse supernovae.
Furthermore, the host galaxies of the long gamma-ray bursts are significantly
fainter and more irregular than the hosts of the core-collapse supernovae.
Together these results suggest that long-duration gamma-ray bursts are
associated with the most massive stars and may be restricted to galaxies of
limited chemical evolution. Our results directly imply that long gamma-ray
bursts are relatively rare in galaxies such as our own Milky Way.Comment: 27 pages, 4 figures, submitted to Nature on 22 August 2005, revised 9
February 2006, online publication 10 May 2006. Supplementary material
referred to in the text can be found at
http://www.stsci.edu/~fruchter/GRB/locations/supplement.pdf . This new
version contains minor changes to match the final published versio
Bone and joint infections in adults: a comprehensive classification proposal
Ten currently available classifications were tested for their ability to describe a continuous cohort of 300 adult patients affected by bone and joint infections. Each classification only focused, on the average, on 1.3\u2009\ub1\u20090.4 features of a single clinical condition (osteomyelitis, implant-related infections, or septic arthritis), being able to classify 34.8\u2009\ub1\u200924.7% of the patients, while a comprehensive classification system could describe all the patients considered in the study. RESULT AND CONCLUSION: A comprehensive classification system permits more accurate classification of bone and joint infections in adults than any single classification available and may serve for didactic, scientific, and clinical purposes
Treatment of Infected Hip Arthroplasty
The clinical outcomes of a consecutive series of deep total joint infections treated with a prosthesis retaining protocol were reviewed. The treatment of deep periprosthetic joint infections is challenging. In recent years, two-stage exchange arthroplasty has emerged as the gold standard for successful elimination of infection. With success rates averaging 82% to 96%, this treatment method has both the highest and most consistent rate of infection eradication. Another alternative in the treatment of the deep periprosthetic infection is the single-stage exchange arthroplasty. Successful eradication of infection after single-stage exchange arthroplasty has been reported to average from 60% to 83% after total hip infections. While both the single and two-stage exchange arthroplasty are viable treatment options, they are associated with negative factors such as they are time consuming, expensive, and may entail a 6- to 12-week period with a minimally functioning extremity after prosthesis removal. This paper reports the general principles of management, the treatment of acute infection occurring in the postoperative period or later, and the treatment of chronic infection by exchange arthroplasty or resection arthroplasty
Alumina-on-Polyethylene Bearing Surfaces in Total Hip Arthroplasty
The long-term durability of polyethylene lining total hip arthroplasty (THA) mainly depends on periprosthetic osteolysis due to wear particles, especially in young active patients. In hip simulator study, reports revealed significant wear reduction of the alumina ceramic-on-polyethylene articulation of THA compared with metal-on-polyethylene bearing surfaces. However, medium to long-term clinical studies of THA using the alumina ceramic-on-polyethylene are few and the reported wear rate of this articulation is variable. We reviewed the advantages and disadvantages of ceramicon- polyethylene articulation in THA, hip simulator study and retrieval study for polyethylene wear, in vivo clinical results of THA using alumina ceramic-on-polyethylene bearing surfaces in the literature, and new trial alumina ceramic-onhighly cross linked polyethylene bearing surfaces
Measurement of the inclusive and dijet cross-sections of b-jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector
The inclusive and dijet production cross-sections have been measured for jets
containing b-hadrons (b-jets) in proton-proton collisions at a centre-of-mass
energy of sqrt(s) = 7 TeV, using the ATLAS detector at the LHC. The
measurements use data corresponding to an integrated luminosity of 34 pb^-1.
The b-jets are identified using either a lifetime-based method, where secondary
decay vertices of b-hadrons in jets are reconstructed using information from
the tracking detectors, or a muon-based method where the presence of a muon is
used to identify semileptonic decays of b-hadrons inside jets. The inclusive
b-jet cross-section is measured as a function of transverse momentum in the
range 20 < pT < 400 GeV and rapidity in the range |y| < 2.1. The bbbar-dijet
cross-section is measured as a function of the dijet invariant mass in the
range 110 < m_jj < 760 GeV, the azimuthal angle difference between the two jets
and the angular variable chi in two dijet mass regions. The results are
compared with next-to-leading-order QCD predictions. Good agreement is observed
between the measured cross-sections and the predictions obtained using POWHEG +
Pythia. MC@NLO + Herwig shows good agreement with the measured bbbar-dijet
cross-section. However, it does not reproduce the measured inclusive
cross-section well, particularly for central b-jets with large transverse
momenta.Comment: 10 pages plus author list (21 pages total), 8 figures, 1 table, final
version published in European Physical Journal
Observation of associated near-side and away-side long-range correlations in âsNN=5.02ââTeV proton-lead collisions with the ATLAS detector
Two-particle correlations in relative azimuthal angle (ÎÏ) and pseudorapidity (Îη) are measured in âsNN=5.02ââTeV p+Pb collisions using the ATLAS detector at the LHC. The measurements are performed using approximately 1ââÎŒb-1 of data as a function of transverse momentum (pT) and the transverse energy (ÎŁETPb) summed over 3.1<η<4.9 in the direction of the Pb beam. The correlation function, constructed from charged particles, exhibits a long-range (2<|Îη|<5) ânear-sideâ (ÎÏâŒ0) correlation that grows rapidly with increasing ÎŁETPb. A long-range âaway-sideâ (ÎÏâŒÏ) correlation, obtained by subtracting the expected contributions from recoiling dijets and other sources estimated using events with small ÎŁETPb, is found to match the near-side correlation in magnitude, shape (in Îη and ÎÏ) and ÎŁETPb dependence. The resultant ÎÏ correlation is approximately symmetric about Ï/2, and is consistent with a dominant cosâĄ2ÎÏ modulation for all ÎŁETPb ranges and particle pT
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